Biology B1


Diet and Exercise

A person is malnourished if their diet is not balanced. This may lead to a person being overweight or underweight. An unbalanced diet may also lead to deficiency diseases or conditions such as Type 2 diabetes.

The metabolic rate varies with the amount of activity you do and the proportion of muscle to fat in your body. Metabolic rate may be affected by inherited factors

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Immune System

White blood cells help to defend against pathogens by:

ingesting pathogens

■ producing antibodies, which destroy particular bacteria or viruses

■ producing antitoxins, which counteract the toxins released by the pathogens.

it is difficult to develop drugs that kill viruses without also damaging the body’s tissues.

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antibiotics kill individual pathogens of the non-resistant strain

■ individual resistant pathogens survive and reproduce, so the population of the resistant strain increases

now, antibiotics are not used to treat non-serious infections, such as mild throat infections, so that the rate of development of resistant strains is slowed down.

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Uncontaminated culture

Uncontaminated cultures of microorganisms are required for investigating the action of disinfectants and antibiotics.

For this:

■ Petri dishes and culture media must be sterilised before use to kill unwanted microorganisms

inoculating loops used to transfer microorganisms to the media must be sterilised by passing them through a flame.

 ■ the lid of the Petri dish should be secured with adhesive tape to prevent microorganisms from the air contaminating the culture.

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Hormones / Menstrual cycle

Hormones are secreted by glands and are usually transported to their target organs by the bloodstream.

  follicle stimulating hormone (FSH) is secreted by the pituitary gland and causes eggs to mature in the ovaries. It also stimulates the ovaries to produce hormones including oestrogen.

■ oestrogen is secreted by the ovaries and inhibits the further production of FSH. It stimulates the production of LH.

■ luteinising hormone (LH) stimulates the release of eggs from the ovary

■ Progesterone maintains the lining of the uturus 

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Phototropism : When auxin is made at the shady part of a stem so the plant grows towards to light stimulus

Geotropism : When auxin helps a plant grow in response to the force of gravity

Upward growth ofplant shoots = negative geotropism 

Downwards growth = positive geotropism

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Drugs change the chemical processes in peoples’ bodies so that they may become dependent or addicted to the drug and suffer withdrawal symptoms without them

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Competition: limited to light, water, space and nutrients in plants; food, mates and territory in animals.

Extremophiles may be tolerant to high levels of salt, high temperatures or high pressures.

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■ lichens can be used as air pollution indicators, particularly of the concentration of sulfur dioxide in the atmosphere

invertebrate animals can be used as water pollution indicators and are used as indicators of the concentration of dissolved oxygen in water.

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Carbon Cycle

■ carbon dioxide is removed from the environment by green plants and algae for photosynthesis

■ when green plants and algae respire, some of this carbon becomes carbon dioxide and is released into the atmosphere

■ green plants and algae are eaten by animals and these animals are eaten by other animals

■ animals respire 

■ when plants, algae and animals die, some animals and microorganisms feed on their bodies and carbon is released into the atmosphere as carbon dioxide when these organisms respire

combustion of wood and fossil fuels releases carbon dioxide into the atmosphere.

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Darwin's Theory

Darwin’s theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago.

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